Components and production methods for components for impedance change in coplanar waveguides have become known in various specific embodiments.
In one specific embodiment of a micromechanically produced high-frequency short-circuiting switch, a thin metal bridge is stretched between grounding conductors of a coplanar waveguide. This bridge is electrostatically drawn to a thin dielectric disposed on a signal line lying between the ground elements, thereby increasing the capacitance of a “plate-type capacitor” formed by the bridge and the signal line. This capacitance change influences the propagation properties of the electromagnetic waves guided on the waveguide. In the “off” state (the metal bridge is pulled downwards to the signal line) a major part of the power is to be reflected. In the “on” state, however, (the metal bridge is above), a large part of the power is transmitted.
In German Laid-Open Document DE 100 37 785 A1, a device for impedance change on a coplanar waveguide is discussed, in which the grounding conductors are connected by a connecting piece and the signal line has a bridge, at the location of the connecting piece, which, in turn, may be operated electrostatically. The advantage of this specific embodiment is that the length of the metal bridge, that is, the length of the bridge over the element connecting the grounding conductors, is not a function of the clearance between the grounding conductors of the coplanar waveguide. Accordingly, the clearance between the grounding conductors of the waveguide may be selected independently of the length of the bridge, and vice versa,
A disadvantage of both the mentioned specific embodiments is that, for the electrostatic operation of the respective bridge, the grounding conductors and the signal line have to have a direct current control voltage applied to them.
One structure from the related art that does not have this disadvantage is shown in FIGS. 5a and 5b of the attached drawings. FIG. 6 shows, in addition, a greatly schematized equivalent circuit diagram for this structure. Component 101, illustrated in FIGS. 5a and 5b, for impedance change of a section of a waveguide 102 includes two external grounding conductors 103, 104 and a signal line 105 lying between them. A bridge arrangement 106 having a self-supporting bridge 107 is constructed over grounding conductors 103 and 104, as well as signal line 105. A section along section line V-V, having a nondeflected bridge 107 and a deflected bridge 107 (drawn in broken lines) is illustrated in FIG. 5b. Bridge 107 is stretched between vertical member elements 108 that are electroplated on at each end.
In order to obtain a compact structure, each grounding conductor 103 and 104 has a recess 103a or 104a in the vicinity of bridge 107.0
The bridge, via a connection 109, may have applied to it a control dc voltage with respect to lines 103, 104, 105, in order to draw the bridge against lines 103, 104, 105 via electrostatic forces. To avoid a short circuit, in the vicinity below the bridge, an insulating layer 110 is laid over lines 103, 104, 105 (for this, see especially the sectional arrangement).
Component 101 may be described by an equivalent circuit diagram according to FIG. 6, with a view to its high frequency properties. Symmetrical to two line sections 111, 112 with symbolically shown characteristic wave resistance 113, a grounded branch 114 branches off, which has the following components: A first mutual capacitance 115, an inductance 116 and an ohmic resistance 117, followed by a second mutual capacitance 118. Before the second mutual capacitance, a voltage source 119 is symbolically connected.
First mutual capacitance 115 is defined by the intersection of signal line 105 and 107, and may assume, in particular, two capacitance values according to the two positions shown in FIG. 5b. Inductance 116 comes about from the bridge sections between signal line 105 and respective grounding conductor 103, 104. The same sections define ohmic resistance 117. Mutual capacitance 118 is established by the intersection of bridge 107 with the respective narrow region of grounding conductors 103 or 104, and may also, just as first mutual capacitance 114, in particular, assume two values corresponding to the positions of bridge 107 shown in FIG. 5b. Using such a construction, one may achieve, for example, a capacitance change by approximately a factor of 100, whereby component 101 may be used in a prespecified frequency range as a high frequency switch.
In principle, using this construction, a decoupling of the control signal of the switchable capacitances of lines 103, 104, 105 is implemented, and thereby the possibility is given of using such switching elements in change-over switches, distribution networks or phase shifters.
However, it has turned out that such a bridge, having uniformly reproducible switching properties, is not simple to implement, if it can be done at all.